International organizations’ (IOs) power in shaping global governance outcomes is not only determined by the formal delegation of tasks and issue areas but also by the necessary capabilities to fulfill these tasks. Yet, extant research on the delegation of power to IOs gives few insights into the financial and staff capabilities of IOs and focuses mainly on the formal rules that specify IOs’ tasks and issue scope. To address these limitations, this paper makes three contributions. First, we propose a more encompassing concept of IO power which incorporates three principal components: tasks, issue scope, and capabilities. Second, we introduce a new concept – IO empowerment (IOE) – which encapsulates formal and informal changes in IO power over time. Third, we introduce a novel dataset on IO capabilities, which measures the formal rules governing IO staff and financial resources as well as the actual capabilities available to six well-known IOs over 65 years. These original data show that capabilities vary not only across IOs but also over time.